# Integrating with react-dates

[react-dates](https://github.com/airbnb/react-dates) is a fantastic date-picker library from AirBnB. It is built on top of Aphrodite and comes with monolithic class names by default in order to be unopinionated regarding the styling layer.

Here is how to integrate it properly with Fela so styles are applied atomically with Fela (and therefore optimised) instead of through the original CSS classes.

It offers a way to customise the rendering process with [react-with-styles](https://github.com/airbnb/react-with-styles) interfaces. The idea is to write a `react-with-styles` interface for Fela. Then, the interface can be registered against `ThemedStyleSheet` from `react-with-styles`.

```js
import ThemedStyleSheet from 'react-with-styles/lib/ThemedStyleSheet'

ThemedStyleSheet.registerInterface(FelaInterface)
```

It needs the Fela renderer as an argument in order to compute resolved class names.

```js
import { StyleSheet } from 'fela-tools'
import { combineRules } from 'fela'

// Custom `react-with-styles` interface for Fela:
// https://github.com/airbnb/react-with-styles
export default (renderer) => ({
  create(styleHash) {
    return StyleSheet.create(styleHash)
  },

  resolve(stylesArray) {
    const styles = stylesArray.flat()
    const rules = []
    const classNames = []

    // This is run on potentially every node in the tree when rendering,
    // where performance is critical. Normally we would prefer using
    // `forEach`, but old-fashioned `for` loops are slightly faster.
    for (let i = 0; i < styles.length; i += 1) {
      const style = styles[i]

      if (!style) continue
      if (style.ruleName) classNames.push(style.ruleName)
      if (typeof style === 'function') rules.push(style)
      else rules.push(() => style)
    }

    const rule = combineRules(...rules)
    const classes = renderer.renderRule(combineRules(...rules))

    classNames.push(classes)

    return { className: classNames.join(' ') }
  },
})
```
